Fastener Nomenclature and Designation System Explained

Fastener nomenclature is the standardized method used to identify and specify fasteners such as bolts, screws, nuts, washers, and studs. It typically includes the product type, applicable standard, thread size, length, material grade, mechanical property class, and surface finish.

Standardized fastener designation eliminates ambiguity, ensures interchangeability between manufacturers, simplifies procurement, and helps maintain compliance with engineering and quality standards.

The designation M10×50 indicates a metric fastener with a nominal thread diameter of 10 mm and a nominal length of 50 mm. If the thread pitch is omitted, the standard coarse pitch is generally assumed.

Property class 8.8 identifies the mechanical strength of a carbon steel fastener. The first number multiplied by 100 gives the nominal tensile strength (800 MPa), while the product of both numbers multiplied by 10 gives the approximate yield strength (640 MPa).

A2-70 refers to an austenitic stainless steel fastener. A2 generally corresponds to stainless steel grade 304, while 70 indicates a minimum tensile strength of 700 MPa.

Zn indicates that the fastener has a zinc-plated surface finish, which provides corrosion protection and improved appearance.

DIN standards originated from the German Institute for Standardization, while ISO standards are international standards developed by the International Organization for Standardization. Many traditional DIN fastener standards have been replaced by equivalent ISO standards.

Fastener length measurement depends on the fastener type. For example, hex bolts are measured from the bearing surface under the head to the end of the fastener, while countersunk screws are measured including the head.

Coarse threads use a larger thread pitch and are suitable for general applications, while fine threads have a smaller pitch and provide greater adjustment accuracy, higher tensile stress area, and improved resistance to loosening.

No. The elements included in a fastener designation depend on the specific product standard and application requirements. However, critical characteristics such as thread size, length, material or property class, and surface finish should be specified whenever applicable.

The applicable standard is usually specified in engineering drawings, customer specifications, or industry standards. Common examples include DIN 933 / ISO 4017 for hex bolts, DIN 934 / ISO 4032 for hex nuts, and DIN 125 / ISO 7089 for plain washers.

Although many DIN standards have been superseded by ISO standards, the original DIN designations remain deeply embedded in engineering drawings, procurement systems, catalogs, and industry terminology, and therefore continue to be widely used throughout the world.